In general, image forming apparatuses, such as, for example, printers, copiers, and facsimile machines, print documents using an electro-photographic developing method in which an electrostatic latent image on an image bearing unit is developed to produce a toner image that is then transferred to a printing medium.
To print documents using the electro-photographic developing method, an image forming apparatus cam include multiple rollers having diverse functions. Among such rollers are, for example, conductive rollers that receive an electrical power, an example of which may be a toner supply roller.
The toner supply roller is a roller configured to supply toner to a developing roller positioned opposite the toner supply roller. To transfer the toner to the developing roller using electrical attraction as well as contact friction, the toner supply roller can receive an electrical power to generate an electric potential difference with the developing roller.
The toner supply roller can be generally formed in one of two types: a sponge-type supply roller or a fiber-type supply roller. A sponge-type supply roller can be made of a foaming rubber such as silicon or urethane, for example. A fiber-type supply roller can be made by implanting multiple fibers on the external surface of the toner supply roller.
For a sponge-type toner supply roller, having uniformly formed foaming cells on the surface of the sponge-type toner supply roller is important to uniformly supply a toner onto the surface of the developing roller. Because it is not easy to effectively manage the foaming rate, manufacturing toner supply rollers that have a uniform electrical resistance, hardness of the surface, and the number of cells can be difficult to achieve.
For a fiber-type toner supply roller, acrylic fibers or nylon 6 fibers are generally used. To improve upon the performance that can be achieved with sponge-type toner supply rollers, there has been a growing interest in research and development of uniform density of fibers for fiber-type toner supply rollers made of acrylic fibers or nylon 6 fibers.
Research and development effort for improving conductivity of the toner supply roller has not been performed with a similar effort. For example, rollers implanted with nylon 6 fibers can have the electrical resistance changed according to changing ambient conditions, such as changes in temperature and the humidity, for example, that can result in sudden increases in the electrical resistance.
When the electrical resistance of the toner supply roller cannot be maintained at a constant value, the supply of toner to the developing roller may be erratic, possibly resulting in a deterioration of the printing quality and/or an irregular amount of toner consumption.
Therefore, the stable conductivity of the toner supply roller and/or of other conductive rollers in the image forming apparatus is desirable.